Electrode coating



Patented Mar. 20, 1951 UNITED STATES PATENT OFFICE ELECTRODE COATING Paui'J. Hagelston, Danvers, and Robert S. Ives, Topsfield, Mass., assignors to Sylvania Electric Products Inc., Salem, Mass., a corporation of Massachusetts No Drawing. Application February 8, 1946, Serial No. 646,494

1 Claim.

A further object is to provide an electrode with a coating of electron-emissive material which will be substantially completely activated when the gaseous discharge device is operated at relatively low voltages.

Further objects, advantages, and features will be apparent from the following description of the electrode of our invention.

In the manufacture of fluorescent lamps having a filamentary electrode disposed adjacent the ends thereof it has been the practice to apply to the electrode a coating of electron-emissive material. This material usually comprises a carbonate of one or more of the alkaline earth metals, and, in the processing of the lamp, the electrode is heated sufficiently to cause the carbonate to break down and leave a coating of alkaline earth oxide on the cathode.

Lamps of this type, having filamentary electrodes, are operative at relatively low voltages,

such as of the order of 110 to 120 volts.

Electric gaseous discharge tubes having a coating of luminescent material on the walls thereof, and cold cathodes, and which are used as light sources normally are operated at voltages substantially higher than 120 volts, such as, for example, 400-500 volts and higher.

Electric gaseous discharge devices of the glow lamp type having a so-called cold cathode as distinguished from those of the filamentary type and operated at relatively low voltages have not heretofore been generally used as light sources.

In attempting to develop a fluorescent Christmas tree lamp having a round or pear-shaped bulb, a coating of luminescent material on the wall thereof and cold cathodes considerable difiiculty was encountered in developing an electronemissive coating for the cathode which would enable the lamp to operate satisfactorily at low voltages. Coating the cathode with a carbonate of the alkaline earth metals proved unsatisfactory because it was not practical to apply enough heat to the cathode coating to break down the carbonate. When sufficient heat to accomplish the breakdown of the carbonate was applied, the luminescent coating on the wall of the bulb adjacent the cathode became discolored because the base element of the cathode started to decompose.

In attempting to overcome this problem, peroxides of the alkaline earth metals were tried instead of the carbonates because they do not require as much heat to be broken down. A1-

though this change obviated the above-mentioned undesirable condition, a new undesirable condition was noted. An acetate such as amyl acetate is usually used as the vehicle in which the alkaline earth metal peroxide is suspended. Amyl acetate contains a small amount of water and barium peroxide (the particular alkaline earth metal peroxide used) reacts with water as follows:

Barium hydroxide is a compound which is very difficult to break down to a suitable electronemissive coating. The breakdown of amyl acetate-milled barium peroxide was spotty and the lamps made with a cathode coating of this composition usually required relatively long aging periods.

We have found that a product having highly desirable characteristics may be obtained by using a hydrophobic vehicle chemically inert to the peroxides of the alkaline earth group, as the suspension medium. A solvent possessing these characteristics may be selected from one of the following groups: aromatic hydrocarbons, aliphatic hydrocarbons, or saturated halogenated aromatic or aliphatic hydrocarbons. We have found xylol, toluol, and normal heptane to give highly satisfactory results. When vehicles of this type are used they obviate the difficulties mentioned above because they are immiscible with water and they are chemically inert with respect to the peroxides of the alkaline earth group. The fact that they are not miscible with water prevents the formation of a hydroxide, which is difficult to break down to a suitable electron-emissive coating.

What we claim is:

A coating suspension for electric gaseous discharge device electrodes consisting essentially of barium peroxide and avehicle selected from the group consisting of xylol, toluol and normal heptane.

PAUL J. HAGELSTON. ROBERT S. IVES.

REFERENCES CITED The following references are of record in the file of this patent:

Great Britain of 1863 

